Photogrammetry may be defined as the art or science of obtaining reliable information about physical objects through the technique of recording, measuring and interpreting photographic images and, although photogrammetry has been recently expanded to include analysis of other types of sensing, photographs remain as the principal source of information. In metric photogrammetry, precise measurements and computations are made to determine the size and shape of objects photographed, these photographs being normally exposed so that the field of view covered by each successive photograph overlaps or partially duplicates a part of the coverage from the previous photo, but from a different camera position. Thus an overlapping pair of photographs is generally termed a "stereo pair". Photogrammetry may either be aerial or remote; i.e. when taken from an airborne camera or other remove point; or may be terrestrial or "close-range" when taken from an earth-based camera which is relatively near the object to be photographed. Customarily, photogrammetry has been employed for the preparation of planemetric and topographic maps from aerial photography. More recently however such technology has been applied to the measurement of objects at close range; and the present invention is directed primarily to a solution of problems associated with close range photogrammetry.
It is generally known that laterally contiguous photographs can be taken at uniform distances from a desired plane in order to assemble a photomosiac of objects in that plane. For instance, in aerial reconnaissance work, determination of the subject-to-image distance is possible through various mathematical controls requiring computation before or after each exposure is made in order to match adjacent photographs. However, the advantage of extensive coverage provided by remote camera platforms is offset by the limitations of commercially available photosensitive materials which will adequately record the images; also remote camera platforms rely to a great extent on good weather and sunshine for the desired lighting of the subject. On the other hand, in close-range photogrammetry, often meaningless parts of the instruments or their shadows are in the field of view. Interiors, confined spaces, walls and vertical faces are inaccessible to close-range camera platforms and in most cases such devices are capable of photographing only on a horizontal or substantially horizontal plane. Further, while being ground-supported, close-range camera mounts are not fixed rigidly and a series of cameras are required to simultaneously photograph a desired subject for multispectral exposures. Moreover, either in aerial or close-range photogrammetry, when correct photographic exposure of the photosensitive materials is dependent upon a determination of the intensity of natural, atmospheric or solor radiation, that radiation is subject to numerous influences beyond the control of the operator and which are difficult to measure or calculate, especially when recording is done in bands or segments of the electromagnetic spectrum which is invisible to the human eye. Accordingly, it is highly desirable to provide a camera sensing module specifically adaptable for close-range photogrammetry which is portable, compact, self-contained and easily operated, manuevered and controlled. Further in close-range photogrammetry, it is desirable to minimize to the point of substantially eliminating mathematical computations so as to permit simple and inexpensive photogrammetry techniques to be applied and to avoid reliance upon spacial rectification procedures before or after photographing relatively uniform surfaces. Although overlapping or stereo pairs of photographs can be easily obtained for precise determination of object locations through high order post-exposure measuring instruments, it is desirable to provide a simple, relatively inexpensive sensing module and technique which emphasizes more the advantages of increased spectral or color resolution through precisely controlled lighting of the subject in close proximity to the camera and to place all camera controls as well as that segment of the subject area to be photographed within the direct reach of a single operator.